Proteolytic enzymes participate both in the digestion of proteins and in the regulation of their physiological functions. Regulation is mediated by limited proteolysis of zymogens and related protein precursors. Many of these regulatory proteases are homologous and related in structure and enzymatic mechanism to the pancreactic serine proteases. The present program will deal with the following aspects of the regulation by proteases and their chemical structure: (1) Determination of the covalent structure of zymogens involved in blood coagulation; (2) Identification of the changes in protein structure and conformation which occur upon activation of model zymogens (e.g. trypsinogen, chymotrypsinogen, plasminogen, blood coagulation factors); (3) The role of limited proteolysis in fertilization; (4) Studies of the cellular origin of enterokinase and its role in the activation of pancreactic zymogens; (5) Investigation of the transient precursor forms of secretory proteins ("pre-proteins") during protein biosynthesis; (6) Studies of the covalent structure specificity and kinetics of group-specific proteases; (7) Determination of the amino acid sequence of rabbit muscle phosphorylase b, human carboxypeptidase A, crayfish trypsin, and neutral metalloendopeptidase A of B. subtilis; (8) Methodological development of sequence analysis in the nanomole range.